1. Field of the Invention
The present invention is generally related to a control system for a marine engine and, more particularly, to a control system which takes specific actions during an engine shutdown procedure to avoid water inversion through the exhaust system and into the engine cylinders.
2. Description of the Prior Art
Certain known types of gasoline engines are designed in such a way that both the intake and exhaust valves can simultaneously be opened because of an intentional overlap in their respective opening and closing sequences. The purpose of the overlap is to permit more efficient evacuation of exhaust gases from the engine's cylinders. However, this technique can result in a negative pressure within the intake system, between the throttle and the cylinders, when the engine is operating at idle speed. This negative pressure, during an engine shutdown procedure, can be connected in fluid communication with the exhaust system if the intake and exhaust valves are simultaneously open and, as a result, can draw water in a reverse direction through the engine's exhaust conduits from a body of water in which the marine vessel is operating and cause that water to flow into the engine's cylinders. This situation represents one mechanism by which water can be drawn into the power cylinder and is known to those skilled in the art as “water reversion” or “water ingestion”. This ingestion of water into the cylinders can be significantly deleterious to the operation of the engine and, if it results in water lock within the cylinders, can result in a potentially catastrophic failure.
If an engine stops operating with its intake and exhaust valves opened simultaneously in any cylinder, the negative pressure that exists between the throttle plate of the intake manifold and the intake valve can be connected directly through the combustion chamber to the exhaust manifold. This connection of a reduced pressure, which is less than atmospheric pressure, to the exhaust manifold can cause water to be drawn in a reverse direction through the exhaust system and into the cylinder. The magnitude of the negative pressure (i.e. less than atmospheric pressure) and the volume of air at that negative pressure between the throttle plate and the intake valve combine to determine the degree with which water is drawn in a reverse direction through the exhaust system. If the volume between the throttle plate and the intake valves is significant, and the negative pressure is sufficient, enough water can be drawn upwardly through the exhaust system to cause some of that water to flow in a reverse direction through the exhaust valve and into the power cylinder. Those skilled in the art of marine propulsion systems are familiar with this concept. Many different techniques have been used in an attempt to inhibit water reversion or water ingestion and lessen its potential deleterious effects.
U.S. Pat. No. 6,077,137, which issued to Hahn on Jun. 20, 2000, describes an anti-ingestion device for use with an engine, preferably a marine engine. The device comprises an exhaust manifold or riser system for exhausting engine gases, wherein the exhaust manifold has a first end and a second end, and the first end is connected to a cylinder head. There is a one-way pressure relief valve having a first end and a second end, wherein the first end is coupled to the exhaust manifold and the second end is exposed to atmospheric pressure.
U.S. Pat. No. 5,558,549, which issued to Nakase et al. on Sep. 24, 1996, describes a four cycle engine for a watercraft. Induction and exhaust systems are provided for the engine which includes position responsive valves that close when the watercraft is inverted to preclude from entering the combustion chamber through either the intake or the exhaust system.
U.S. Pat. No. 5,324,217, which issued to Mineo on Jun. 28, 1994, describes an exhaust system for a small watercraft which includes a water trap device for precluding water from entering the engine through the exhaust system if the watercraft becomes inverted, from entering.
U.S. Pat. No. 4,350,010, which issued to Yukishima on Sep. 21, 1982, describes an exhaust system for an outboard engine which has a casing, an internal combustion engine and a water cooling circuit and an exhaust pipe. The exhaust pipe discharges exhaust gases into an expansion chamber and gases from the expansion chamber are discharged into the body of water in which the vessel propelled by the engine floats. The exhaust pipe projects into the expansion chamber and has pores near its outlet end. Coolant water is discharged into the expansion chamber and mixes with the exhaust gases. Gas flow through the pores discourages reverse flow of water droplets through the exhaust pipe to the engine cylinders.
U.S. Pat. No. 3,552,121, which issued to Kitagawa et al. on Jan. 5, 1971, describes a means for preventing reverse water flow through an exhaust pipe of a rotary piston type marine engine. A reverse water flow arrester for a Wankel type rotary piston engine having an exhaust pipe with one end connected with an exhaust working chamber of the engine and the other end inserted into water for discharging exhaust gas thereinto, said arrester comprising a vacuum valve for relieving negative pressure created during engine start within the engine exhaust working chamber in order to prevent the water taken into the engine due to negative pressure and means for interconnecting the vacuum valve with engine starting means to open the valve during engine start.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.